The present invention relates in general to communication switching systems and more particularly to a method for minimizing total toll call costs for a distributed network of PBXs.
It is well known in present day PBXs to provide Automatic Route Selection (ARS) or Least Cost Routing (LCR) for outgoing calls. Normally, the call processing necessary to fulfill these functions includes a table look-up of trunks identified by a plurality of exchanges and the costs of making calls over the respective trunks. In a simple system, the trunks are ranked in order of priority. In more complex systems, alternate routings are provided when the least cost route is busy or during specified times of day.
U.S. Pat. No. 5,675,636 (Gray) provides an Automatic Route Selection (ARS) algorithm whereby the decision on call assignments to trunks is done dynamically, rather than being done according to a fixed plan or route list. Consequently, advantage can be taken of dynamic revaluation of route plans in relevant circumstances such as call volume discounts. The invention is implemented using software agents which bid to have calls assigned to their trunks by means of poking tuples and anti-tuples into tuple space (i.e. shared memory).
Although the aforenoted patent of Gray provides a solution for minimizing costs in a stand-alone PBX environment, many enterprises utilize a distributed network of PBXs. Considerable cost savings can be achieved in such networked systems utilizing similar features. For example, taking into account tariffs for international calls and tie lines, in some circumstances it may be most cost effective to route a call from one PBX to another PBX in the network and utilize a national toll route rather than an international route directly from the first PBX. For another example, it may be cheaper to direct a call through paid-for private routes through the network of PBXs instead of a toll call from the originating PBX.
It is an aspect of the present invention to provide a method for minimizing total toll call costs for a distributed network of PBXs in which cost information concerning competitive routing plans available at the individual PBXs is shared.
According to the present invention, a method is provided for minimizing the total cost of trunk toll calls for a distributed network of PBXs. An originating PBX proposes a toll call to all connected PBXs in the network and requests the cost of the toll call. Each PBX then proceeds to perform the same task until all possible routes between the originating PBX and a toll call destination is found. Each PBX then proceeds to select the least expensive toll call among the many possibilities (preferably using the method disclosed in U.S. Pat. No. 5,675,636) and informs the originating PBX of the choice. The originating PBX selects the least expensive route and completes the toll call.